1. Field of the Invention
The present invention is generally concerned with high-voltage electric cables and is more particularly concerned with a new dry high-voltage cable termination.
2. Description of the Prior Art
There is already known in the prior art, notably from French patent No. 2 518 837, a high-voltage cable termination essentially comprising a conductive core (conventionally covered with a seminconductive layer), an insulative envelope covering the core, an equipotential screen placed around the envelope and a protective outer sheath. In order to optimize the distribution of the electric field between the screen and the core there are provided a number of layers of high permittivity material and, externally of these, a thin layer of semiconductive material with a non-linear coefficient of conduction, forming a linear voltage distributor, disposed over at least part of the length of the bared insulative envelope of the cable.
This type of termination is conventionally surrounded by a porcelain insulative support and an oil bath is provided inside the porcelain to prevent the presence of air that may ionize in the parts of the termination where the electric field is high.
These supports made from porcelain, a material well known for its fragile nature and absence of flexibility, require extreme care when they are fitted in the field and are therefore disadvantageous from this point of view. They are also heavy, bulky and costly.
Also, the presence of oil which is usually necessary when high voltages are involved (typically 150 kV and higher) is disadvantageous in that leaks are always possible and in that its high coefficient of expansion produces high mechanical stresses in the termination.
Moreover, if dielectric breakdown occurs, the oil may ignite and cause a fire.
An object of the present invention is to alleviate these disadvantages and to propose a new high-voltage cable termination comprising no porcelain and no oil and offering great flexibility of use in the field.
Another object of the invention is to confer a self-supporting nature on a high-voltage cable termination. Thus, over and above the electrical connection function, it may serve as a mechanical support for a hollow cylindrical distribution bar made of light alloy as conventionally associated with an isolator or a circuit-breaker.